A well-known multiple-type air conditioner is configured to have a plurality of indoor units connected to the single outdoor unit. During warming operation of the multiple-type air conditioner, the indoor expansion valve is used for controlling the heat exchanger outlet supercooling degree as a measure for adjusting each amount of heat exchanged by the respective indoor units. The supercooling degree is obtained as a difference between a saturation temperature derived from the pressure at the discharge side of the compressor and the refrigerant outlet temperature at the outlet of the indoor heat exchanger for the respective indoor units during warming operation. The heat exchanger outlet supercooling degree control is designed to control the opening degree of the indoor expansion valve to a predetermined value so that the above-described supercooling degree is within a suitable range.
In many cases, a plurality of indoor units for the multiple-type air conditioner will be installed on different floors of the building. In the case that values of the height difference and the piping length deviate from the predetermined range relative to the outdoor unit because of different floors on which those indoor units are installed, the refrigerant supercooling degree at each outlet of the indoor heat exchangers for the respective indoor units cannot be appropriately controlled. This may cause the problem of failing to appropriately control each amount of heat exchanged by the respective indoor units.
Japanese Patent Application Laid-Open No. 2013-178058 (Patent Literature 1) discloses the method for solving the above-described failure. The method employs the first temperature sensor for measuring the liquid piping temperature at the outdoor unit side, and the second temperature sensor for measuring the refrigerant outlet temperature of each indoor heat exchanger for the respective indoor units. The difference between temperatures detected by those sensors during warming operation is obtained. The indoor unit having the temperature difference in excess of the predetermined value is controlled so that the valve opening degree of the indoor expansion valve is opened by a given degree. The disclosed method ensures to maintain the amount of heat exchanged by the indoor heat exchanger appropriately irrespective of the installation state (difference in height, piping length, and the like) of the indoor unit of the air conditioner.